Positive Displacement Pumps

Positive displacement pumps mechanically move a set volume of liquid for each discharge cycle. These pumps have a cavity that expands on the suction side and a decreasing cavity on the side that discharges the material. Positive displacement pumps are divided into two main categories, reciprocating pumps and rotary pumps.

Reciprocating pumps include diaphragm pumps, but also includes plunger pumps. Rather than a diaphragm, the cavity is enlarged or decreased by a reciprocating plunger in the head of a cylinder.

As the plunger retracts, suction valves open to draw fluid into the cylinder. The plunger’s forward stroke pushes the liquid through the discharge valves. Diaphragm pumps operate similarly, but since the liquid does not come into contact with any piston or gears, this pump is especially useful to move hazardous fluids or liquids carrying varied amounts of solid material that could erode and damage pistons or gears in other pumps.

Typical rotary pumps include:

gear pumps

lobe pumps

vane pumps

progressive cavity pumps

peripheral pumps

screw pumps

Rotary pumps move fluid driven by internal gears, screws, vanes or rotating pistons. Gear and screw pumps trap liquid as the teeth open between two identical, continually rotating gears, and squeeze out the fluid when the gears complete a rotation and turn against each other. Lobe pumps operate similarly, driven by external timing gears. Progressive cavity and vane pumps use a cylindrical rotor in a casing. Vanes trap liquid between the rotor and the casing to draw it through the pump.

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Red Seal Measurement systems are specially designed to provide unsurpassed service in the most demanding measurement applications, from refined fuel custody transfer to exacting batching operations in the food and chemical industries.